High-q loading coil having plural interleaved paralleled windings in combination with axial antenna



TAYLOR July 23, 1963 J. 3,099,010

HIGH-Q LOADING COIL HAVING PLURAL INTERLEAVED PARALLELED WINDINGS IN COMBINATION WITH AXIAL ANTENNA Filed Feb. 19, 1960 OQN Own 1 Own IN V EN TOR. JOHN F: no

A rro /vs vs United States Patent 3,090,010 HIGH-Q LOADING COIL HAVING PLURAL INTER- LEAVED PARALLELED WINDINGS IN CGMBI- NATION WITH AXIAL ANTENNA John Taylor, Columbia, S.C., assignor to Coiurnhia Products Company, Columbia, S.C., a corporation of South Carolina Filed Feb. 19, 1960, Ser. No. 9,792 5 Claims. (Cl. 343-749) This invention relates to a novel dipole antenna structure and more particularly to a high Q antenna loading coil.

As is well-known, it is desirable that an antenna loading coil have a high Q, i.e. a low resistance, in order to minimize the energy dissipated in the resistance of the coil, so that the radiation efiiciency will be of a high order of magnitude. In loading coils of the usual type having a single wire Wound about a core it has been found that the Q in many instances is not as high as desired. Several methods have been tried to reduce the resistance of the coil. For example, it has been found that the resistance of the coil can be decreased by using a conductor which has more surface area. A flat wire with rectangular cross-section, or several Wires of circular cross-section can be used, although the reduction of resistance by either of these methods is not as pronounced :as would be expected by the increase in surface area. With the rectangular wire the current tends to be concentrated near the edges with very little current flowing hear the center of the fiat surfaces. With the parallel combination of circular wires most of the current tends to flow in the outside Wires. Thus with either of the latter two methods, the surface area is not fully utilized.

It is an object of the present invention to provide an antenna loading coil in which the structural symmetry of the coil is utilized to force the radio frequency current to divide equally among a plurality of wires and thus make more eflicient use of the available cross-section in reducing the resistance of the coil.

Another object is to provide a dipole antenna having the loading coil built directly into the antenna and receiving protection as well as structural reinforcement therefrom.

Briefly the loading coil of the present invention is a single layer coil having three conductors interwound in the same plane about a common core and disposed at axially spaced positions along said core. Each of the conductors has axially extending straight portions at each end and the respective straight portions of the three conductors are disposed 120 apart relative to one anotheraround the core. Conductive bands are disposed around the periphery of the core at each end thereof and are electrically interconnected with the respective conductor ends at circumferential points 120 apart on said bands.

In the antenna structure the loading coil is disposed in coaxial relation with the antenna structure core at an intermediate portion along the length thereof and the coil is embedded in the structure with its straight conductor portions being symmetrically spaced in a circumferential direction relative to one another about the antenna core. The antenna conductor extends longitudinally in the dipole antenna and is connected at its inner end to one of the conductive bands of the coil and means is provided for the other of said conductive bands for operatively connecting it to radio apparatus or the like.

Other objects and features of the invention will become apparent in the following specification and claims and in the drawings in which:

FIGURE 1 is an enlarged elevation of a loading coil according to the present invention;

FIGURE 2 is a plan View of the device shown in FIGURE '1;

FIGURE 3 is an elevation of a dipole antenna embodying the loading coil of the present invention; and

FIGURE 4 is a graphical plot of Q vs. frequency in megacycles.

Referring now the drawings a loading coil according to the present invention is shown in FiGURE 1 and designated generally by the reference numeral 10. It is comprised of a cylindrical core 11 having metallic bands or caps 12 at either end thereof. Inter-wound around the periphery of the core 11 are three conductors 13, 14 and 15 respectively which are disposed at axially spaced positions as shown to provide a single layer coil having three interspersed conductors tor wires. The ends 16 of the respective conductors are attached by suitable means to the conductive bands or caps 12 at positions relative to one another on the periphery of said bands (see also FIGURE 2). Axially extending conductors 17 are afi-lxed centrally on the conductive caps 12 as shown to provide interconnection with the antenna circuitry.

The conductors employed in winding the coil 10 may be of any desired size and geometry as dictated by the particular requirements and they may be wound in a symmetrically spaced relation as shown in FIGURE 1 or placed side-by-side and touching one another, the difference in results being discussed hereinafter. In order to demonstrate the advantages of winding a coil by the method herein described, several coils were wound for a length of ten inches on a one inch diameter mandrel. The coil and mandrel were then coated with fiberglass and the mandrel extracted. Each conductor was wound at a pitch of five turns per inch. The coils were as follows:

(1) A single #18 tinned copper wire.

(2) Two #18 tinned copper wires side-by-side and touching each other.

(3) Two #18 tinned copper wires symmetrically placed as in the described method.

(4) Three #18 tinned copper wires side-by-side and touching each other.

(5) Three #18 tinned copper wires symmetrically placed as in the described method.

(6) One bare copper wire of rectangular cross-section 0.100 x 0.035" wound with a flat side to the mandrel.

Each of the coils had an inductance of approximately 5.5 rnicrohenries. The values of Q obtained are shown in FIGURE 4. It can be seen that maximum Q was obtained for each coil at approximately eight megacycles and the highest Q coil was the three wire symmetrically spaced coil which gave a peak value of approximately 330 at about eight megacycles. By contrast the one wire coil gave a peak value of about 220 at the same frequency.

It can thus be seen that by symmetricmly spacing the three conductors at 120 positions around the periphery of the conductive bands the coil current is distributed substantially uniformly among the three conductors and the effective surface area of the coil is thereby significantly multiplied with a concomitant reduction in coil resistance.

In use with a dipole antenna the instant coil can be built into the antenna itself. For example, in the dipole antenna 18 as shown in FIGURE 3 the coil can be wound on a fiberglass antenna core 19 at an intermediate portion along its length and then covered with an outer fiberglass coating 20. A coil of the type shown in FIG- URE 1 can be employed or a somewhat modified form as shown in FIGURE 3 in which the conductors of the coil have axially extending straight portions 21, 22 at each end, the respective straight portions being symmetrically spaced in a circumferential direction relative to one another about the core 19. The conductive bands or caps 12 are mounted on the core 19' and have the conductor ends connected therewith at symmetrically spaced points, e.g. at 120 intervals, around the periphery thereof. Antenna conductor 23 is affixed centrally with respect to the conductive cap 12 at its inner end and extends upwardly through the fiberglass rod of the antenna as shown. Conductor means 24 is similarly affixed to the lower conductive band 12 and extends outwardly from the bottom 25 of the dipole for interconnection with radio apparatus and the like in the well-known fashion.

The antenna comprises a substantially uniform outer layer 20 which consists of a plurality of longitudinallyextending glass fibre members. These fibres are very fine and may have diameters of approximately two microinches and a tensile strength of approximately 300,000 pounds per square inch.

Within the outer layer is an inner layer or core 19' of circumferentially-extending, and in this case, spirallywound contiguous glass fibre members.

All of the fibers are bound each to the next adjacent fibre by means of a suitable flexible plastic resin. A resin of the polyester type which may be cured by the application of heat at approximately 190 F. for approximately four hours is a satisfactory resin. It is applied by coating the glass filaments or fibres prior to the assembly thereof into the shaft.

In the preferred form of the invention parts by Weight of resin are used to coat 70 parts by Weight of glass fibres. This proportion may, however, be varied.

After the fibres are coated, they are assembled on a suitable, tapered mandrel, which is not shown. The glass fibres are spirally wound on the mandrel in contiguous relationship.

Then the coil 10 is wound upon the core 19 to provide the wire form described above. A filament of glass thread impregnated with resin can be placed between the symmetnically spaced wires as the coil is wound. The straight portions of the conductors are then interconnected with conductive bands 12.

Thereafter the outer coat, layer 20, is applied and the entire stick is wrapped in a cellophane strip which compacts the fibres and holds them in the desired shape. They are then cured by the application of heat for the appropriate amount of time at the desired degree of heat to set the resin which had been coated on the fibres prior to their assembly. Thereafter the mandrel is removed, leaving a hollow center in the antenna, and the cellophane strip is likewise removed.

The coil of the present invention thus provides a significant increase in Q that may be utilized in various applications where the skin effect and the like is encountered, as Well as other applications which will be apparent to those skilled in the art. The instant coil can be used in various types of antennas having widely varying frequency ranges.

It is to be understood that vanious changes, additions, substitutions and possible omissions can be made by those skilled in the art without departing from the scope and spirit of the invention.

I claim:

1. A unitary dipole antenna structure comprising an active antenna portion having an axially extending conductor therein and a base portion, a high Q loading coil in said base portion including a plurality of conductors interwound about a common core, each of said conductors having axially extending straight portions at each end, the respective said straight portions being symmetrically spaced relative to one another about said core, conductive means disposed at each end of said base portion and electrically interconnected with the respective ends of said conductors at symmetrically spaced points on said conductive means, said axially extending conductor in said antenna portion electrically connected to the one of said conductive means adjacent said antenna portion, and means on said base portion for operatively connecting the other of said conductive means with radio apparatus.

2. A unitary dipole antenna structure comprising an active antenna portion having an axially extending conductor therein and a base portion integrally formed with said antenna portion, a single layer high Q loading coil in said base portion including three conductors interwound about a common core and disposed at spaced positions therealong, each of said conductors having axially extending straight portions at each end, the respective said straight portions being disposed at relative to one another about said core, conductive bands disposed around the periphery of said core at each end of said base portion and electrically interconnected wtih the respective ends of said conductors at circumferential points lr20= apart on said bands, said axially extending conductor in said antenna portion electrically connected to one of said bands adjacent said antenna portion, and means on said base portion for operatively connecting the other of said bands with radio apparatus.

3. A unitary dipole antenna structure comprising an active antenna portion having an axially extending conductor therein and a substantially cylindrical base portion integrally formed and coaxial with said antenna portion, a single layer high Q loading coil in said base portion including three conductors interwound in the same plane about a common core and disposed at axially spaced positions therealong in a coaxial relation with said base portion, each of said conductors having axially extending straight portions at each end, the respective said straight portions being disposed at 120 relative to one another about said core, conductive bands disposed around the periphery of said core at each end of said base portion and electrically interconnected with the respective ends of said conductors at circumferential points 120 apart on said bands, said axially extending conductor in said antenna portion electrically connected to the one of said bands adjacent said antenna portion, and means on said base portion for operatively connecting the other of said bands with radio apparatus.

4. A unitary dipole antenna having an integrally formed high Q loading coil therein disposed in coaxial relation with said antenna at an intermediate portion along its length, said coil comprised of a plurality of conductors interwound in the same plane about a common core with said antenna and disposed at axially spaced positions along said antenna, conductive means at each end of said coil and electrically interconnected with the respective ends of said conductors at symmetrically spaced points on said conductive means, an antenna conductor disposed longitudinally in said antenna and connected at its inner end to one of said conductive means, and means for operatively connecting the other conductive means to radio apparatus.

5. A unitary fiberglass dipole antenna structure having an integrally formed high Q loading coil therein disposed in coaxial relation with said antenna at an intermediate portion along its length, said coil comprised of a plurality of conductors interwound in the same plane about a common core with said antenna and disposed at axially spaced positions along said antenna, each of said conductors having axially extending straight portions at each end, the respective said straight portions being symmetrically spaced in a circumferential direction relative to one another about said core, all of said conductors being embedded in said antenna structure, conductive means at each end of said coil and electrically interconnected with the respective ends of said conductors at symmetrically spaced points on said conductive means, an antenna conductor disposed longitudinally in said antenna and connected at its inner end to one of said conductive means, and means for operatively connecting the other conductive means to radio apparatus.

References Cited in the file of this patent UNITED STATES PATENTS 342,947 Beale June 1, 1886 873,253 MacGahan Dec. 10, 1907 1,967,881 Green July 24, 1934 2,749,266 Eldred June 5, 1956 2,841,789 Bassett July 1, 1958 2,894,260 Ellis July 7, 1959 2,923,652 Oka Feb. 2, 1960 OTHER REFERENCES Najork: Slide Tuning the 75-Meter Loading Ooil, Radio and TV News, pages 51-53, January 1952. 

4. A UNITARY DIPOLE ANTENNA HAVING AN INTEGRALLY FORMED HIGH Q LOADING COIL THEREIN DISPOSED IN COAXIALLY RELATION WITH SAID ANTENNA AT AN INTERMEDIATE PORTION ALONG ITS LENGTH, SAID COIL COMPRISED OF A PLURALITY OF CONDUCTORS INTERWOUND IN THE SAME PLANE ABOUT A COMMON CORE WITH SAID ANTENNA AND DISPOSED AT AXIALLY SPACED POSITIONS ALONG SAID ANTENNA, CONDUCTIVE MEANS AT EACH END OF SAID COIL AND ELECTRICALLY INTERCONNECTED WITH THE RESPECTIVE ENDS OF SAID CONDUCTORS AT SYMMETRICALLY SPACED POINTS ON SAID CONDUCTIVE MEANS, AN ANTENNA CONDUCTOR DISPOSED LONGITUDINALLY IN SAID ANTENNA AND CONNECTED AT ITS INNER END TO ONE OF SAID CONDUCTIVE MEANS, AND MEANS FOR OPERATIVELY CONNECTING THE OTHER CONDUCTIVE MEANS TO RADIO APPARATUS. 